1) Field of the Invention
This invention relates to polyurethane resins and heat-sensitive recording media (hereinafter called "thermal recording materials"), and more specifically to silicone-modified polyurethane resins excellent in stick-free property, antiblocking property and flexibility and also to thermal recording materials making use of such resins, now U.S. Pat. No. 4,942,212.
2) Description of the Related Art
Polyurethane resins have already found a wide variety of utility as binders for various coating agents, coating compositions and inks, films, formed and molded articles, etc. Polyurethane resins suitable for various applications have been proposed.
These polyurethane resins can be obtained basically by reacting a polyol component, a polyisocyanate component and if necessary, a chain extender. Polyurethane resins of various physical properties have been provided depending on the kinds of these individual components, their combinations and the like.
For some applications of polyurethane resins, for example, heat-resistant layers of thermal recording materials and magnetic recording media, stick-free property to thermal heads, antiblocking property between films themselves, etc. are however required in some instances. In general, sufficient flexibility is also required for these applications in order to permit the formation of thin films.
Introduction of one or more aromatic components and many polar bonds into a polyurethane chain is however indispensable to impart high tack-free property and the like. In many instances, this has led to sacrifice of flexibility.
There is accordingly an outstanding demand for the development of a polyurethane resin excellent in high-temperature tack-free property, antiblocking property and the like and superb in flexibility.